JP2016176540A - Electric actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric actuator which is reduced in cost by reducing the number of part items, and improved in reliability by a whirl-stop mechanism which can suppress wear.SOLUTION: An electric actuator comprises: a whirl-stop ball 20 which extends to an axial direction at an internal periphery of a cylindrical bag hole 14 for accommodating a drive shaft 7 in a housing 2b, has a cross-section circular recessed groove 14a, and is engaged with the recessed groove; and a cage 21 attached to a screw shaft 15. A pocket 23 which penetrates a recess 15b of the screw shaft 15 while responding to the recessed groove 14a, and is formed into a large diameter larger than an outside diameter of the whirl-stop ball 20 is protrusively arranged, a cross-section circular guide groove 24 in which the whirl-stop ball 20 is rollingly accommodated, and which extends to an axial direction at an external periphery of the cage 21, and opposes the recessed groove 14a is formed, the whirl-stop ball 20 is held by the guide groove and the recessed groove 14a in a state that the ball has a clearance, and the screw shaft 15 is held so as to be non-rotatable and movable in an axial direction with respect to the housing 2b.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an electric actuator provided with a ball screw mechanism used in a drive unit of a general industrial electric motor or automobile, and more specifically, a rotation input from an electric motor is transmitted to a ball screw in an automobile transmission or a parking brake. The present invention relates to an electric actuator that converts a linear motion of a drive shaft through a mechanism.

  In electric actuators used in various drive units, a gear mechanism such as a trapezoidal screw or a rack and pinion is generally used as a mechanism for converting the rotational motion of the electric motor into a linear motion in the axial direction. Since these conversion mechanisms involve a sliding contact portion, the power loss is large, and it is necessary to increase the size of the electric motor and increase the power consumption. Therefore, a ball screw mechanism has been adopted as a more efficient actuator.

  Generally, in an electric actuator provided with a ball screw mechanism and configured to enclose a nut in a housing, a non-rotating groove is provided on the inner periphery of the housing in order to provide a detent for suppressing rotation of the nut. Need to be provided, or the inner periphery must be formed into a deformed (non-cylindrical) shape. However, when forming a groove on the inner periphery of the housing or forming a deformed shape by machining, the processing of the elongated housing is difficult, so the total length of the housing is limited, resulting in a longer actuator stroke. There is a problem that it cannot be secured. On the other hand, it may be possible to form a groove in the inner periphery of the housing or mold an irregular shape by molding using a mold, but there is a problem that the mold becomes complicated and high in cost. . In addition, in order to engage the nut with the inner circumferential groove of the housing, it is necessary to provide a protrusion on the nut, and there is a problem that the cost of the nut is unavoidable. Furthermore, both the inner periphery of the housing and the nut shape must be complicated, which leads to an increase in the size of the actuator.

  As a solution to such a problem, an electric actuator as shown in FIG. 9 is known. This electric actuator is movable so as to be axially movable with respect to the housing 51, the screw shaft 56 having a male screw groove 56a formed on the outer peripheral surface thereof, and is disposed so as to surround the screw shaft 56. A nut 53 having an internal thread groove 53a formed on the inner peripheral surface, a plurality of balls 57 disposed so as to roll along a rolling path formed between the opposing screw grooves 56a and 53a, and the housing 51 A guide portion 63 a extending along the inner peripheral surface and a guide member 63 including an engaging portion 63 b that engages with the housing 51 are provided.

  The housing 51 includes a substantially hollow cylindrical main body 51a and a cup-shaped lid member 51b fixed so as to close one end of the main body 51a. A cylindrical output shaft 52, which is a driven member, and a nut 53 connected to the output shaft 52 are disposed inside the main body 51a having a cylindrical inner periphery. The output shaft 52 has a left end protruding from the main body in the figure, and a bag hole 52a is formed at the right end in the figure. The outer periphery of the output shaft 52 is slidably supported by the bush 54 with respect to the main body 51a. In addition, a seal member 55 is disposed adjacent to the bushing 54 and seals between the output shaft 52 and the main body 51a, thereby preventing dust and the like from entering from the outside.

  A screw shaft 56 passes through the inside of the nut 53 and enters the bag hole 52a of the output shaft 52 so as to freely enter and exit. On the other hand, the nut 53 arranged so as to surround the screw shaft 56 is formed with a groove 53b along the axial direction on the outer peripheral lower surface thereof, and includes a nut 53 having a tube-type ball circulation member, a screw shaft 56, a ball 57, and A ball screw mechanism is constituted by the guide member 63.

  A ball bearing 59 is disposed at the end of the main body 51a via a bearing spacer 58, and supports the screw shaft 56 rotatably. The outer ring of the ball bearing 59 is fixed to the bearing spacer 58 by a fixing member 60. On the other hand, the inner ring of the ball bearing 59 is fixed to the screw shaft 56 by a retaining ring 61. Therefore, the screw shaft 56 can only rotate with respect to the main body 51a. A gear 62 is connected to the right end of the screw shaft 56 so as to rotate integrally by serration.

  The guide member 63 formed by pressing the metal plate material includes a linear guide portion 63a that is engaged with the thread groove 53a of the nut 53, and a member that is bent at a right angle with respect to the guide portion 63a at the right end in the drawing. And a joint part 63b. Furthermore, as shown in FIG. 10, a groove-like recess 51c is formed on the right end surface of the main body 51a, and the engaging portion 63b is engaged with a recess 51c having the same width as that of the recess 51c. The surface of the guide portion 63a is subjected to a surface treatment including a coating treatment such as manganese phosphate or zinc phosphate for reducing friction.

  When the operator operates the switch, the rotation shaft of a motor (not shown) rotates, power is transmitted through the speed reduction mechanism, and the screw shaft 56 rotates with it. Here, since the nut 53 is smoothly guided only in the axial direction by the guide member 63 that exhibits a detent function, the rotational motion of the screw shaft 56 is efficient for the axial motion of the nut 53. The output shaft 52 that has been converted and thus connected to the nut 53 can be moved in the axial direction.

  At the time of assembly, the guide member 63 is inserted from the right end of the main body 51a to which the bush 54 is assembled, the tip of the guide portion 63a is inserted into the notch 54a, and the bent engaging portion 63b is engaged with the concave portion 51c of the main body 51a. According to this configuration, the guide member 63 can be easily attached to the main body 51a without using a special tool. Thereafter, the nut 53 and the output shaft 52 are inserted into the main body 51a so that the guide portion 63a is engaged with the groove 53b, and the screw shaft 56 and the like are assembled.

  In particular, when the guide portion 63a is long, if only one of the guide members 63 is supported, the guide member 63 may be twisted on the unsupported side, and the anti-rotation function may be insufficient. Here, the front end of the guide portion 63a is engaged with the notch 54a of the bush 54, so that both ends of the guide member 63 can be fixed to the main body 51a. Therefore, even if the guide portion 63a is long, It is possible to suppress the twist and realize an effective detent function (see, for example, Patent Document 1).

JP 2008-232338 A

  In such a conventional electric actuator, as a rotation stop of the nut 53, a groove 53b for rotation prevention is formed on the outer peripheral surface of the nut 53. The guide portion 63a is engaged with the groove 53b, and the tip of the guide portion 63a is connected to the groove 53b. This is done by engaging the notch 54a of the bush 54. This not only increases the number of parts, but also increases the number of assembly steps and becomes complicated, and it is necessary to have surface properties such as hardness and surface roughness that can withstand the sliding of the mating member. There was a problem that costs increased.

  In addition, the sliding area and resistance between the outer diameter portion of the nut 53 and the guide member 63 are large, and there is a risk that abrasion powder may be generated. However, it is also possible to cause uneven wear without linear motion.

  The present invention has been made in view of such problems of the prior art, and reduces the number of parts to reduce costs, and an electric actuator having improved reliability by a detent mechanism capable of suppressing wear. The purpose is to provide.

  In order to achieve such an object, the invention according to claim 1 of the present invention includes a cylindrical housing, an electric motor attached to the housing, and a rotational force of the electric motor transmitted via the motor shaft. And a ball screw mechanism that converts the rotational motion of the electric motor to a linear motion in the axial direction of the drive shaft via the speed reduction mechanism, and this ball screw mechanism is connected to the speed reduction mechanism, A nut rotatably supported through a rolling bearing mounted on the housing and not axially movable and having a helical thread groove formed on the inner periphery, and a plurality of balls inserted into the nut. And an electric actuator composed of a screw shaft that is coaxially integrated with the drive shaft and has a helical thread groove corresponding to the thread groove of the nut on the outer periphery. A cylindrical bag hole that accommodates the drive shaft is formed, and a non-rotating ball that extends in the axial direction on the inner periphery of the bag hole to form a concave groove having an arc-shaped cross section and engages with the concave groove; A cylindrical retainer mounted on the end of the screw shaft, and an axial guide groove extending in the axial direction on the outer periphery of the retainer and facing the concave groove is formed. The non-rotating ball is rotatably held by the concave groove, and the screw shaft is supported so as to be non-rotatable and axially movable with respect to the housing.

  As described above, the ball screw mechanism includes a speed reduction mechanism that transmits the rotational force of the electric motor, and a ball screw mechanism that converts the rotational motion of the electric motor to the linear motion in the axial direction of the drive shaft via the speed reduction mechanism. The mechanism is connected to the speed reduction mechanism, is rotatably supported via a rolling bearing mounted on the housing, and is supported so as not to move in the axial direction, and a nut having a helical thread groove formed on the inner periphery, and An electric actuator comprising a screw shaft that is inserted through a large number of balls, is coaxially integrated with a drive shaft, and has a spiral screw groove corresponding to a screw groove of a nut on the outer periphery. A cylindrical bag hole that accommodates the drive shaft is formed, extends in the axial direction on the inner periphery of the bag hole, is formed with a concave groove having an arc-shaped cross section, and a detent ball that engages with the concave groove; Attached to the end of the screw shaft A cylindrical retainer and an axially extending guide groove extending in the axial direction on the outer periphery of the retainer and facing the concave groove. The guide groove and the concave groove allow rotation of the anti-rotation ball. Non-rotating mechanism that can be held freely and the screw shaft is supported so that it cannot rotate with respect to the housing and can move in the axial direction. Thus, an electric actuator with improved reliability can be provided.

  Preferably, as in the invention according to claim 2, a recess is formed at an end of the screw shaft, and the outer diameter of the detent ball is penetrated from the outer diameter to the recess corresponding to the recess. A pocket formed with a larger diameter than the cylindrical portion, the non-rotating ball is rotatably accommodated therein, and the retainer is fitted into a recessed portion of the screw shaft, and the cylinder If one end part of the part has a flange part extending radially outward, and the flange part abuts the end surface of the screw shaft and the retainer is positioned and fixed, the detent ball is moved in the circumferential direction. As a result, the assembly performance can be improved, the number of parts can be further reduced, and the cost can be reduced.

  According to a third aspect of the present invention, a small diameter step is formed at the end of the screw shaft, the retainer is fitted on the small diameter step, and the outer diameter of the retainer is cylindrical. A retaining ring is press-fitted, and the detent ball is rotatably accommodated in a pocket formed through the inner and outer diameters of the retaining ring. The retainer is a stepped portion of a small-diameter stepped portion of the screw shaft. If the retainer is positioned and fixed in contact with each other, the sliding friction and wear of the housing can be reduced, the assemblability can be further improved, and the cost can be reduced with a simple structure.

  Further, as in a fourth aspect of the present invention, if a plurality of the anti-rotation balls are arranged at positions that are equally spaced around the circumference, even if a load is applied to the screw shaft, The center of the cage can be prevented from being eccentric, and the rotational accuracy of the nut and the straight advance accuracy of the screw shaft can be improved.

  Further, as in the invention described in claim 5, if the cross-sectional shape of the concave groove of the bag hole is formed in a Gothic arc shape or a circular arc shape, when the load is applied, the groove shoulder portion of the anti-rotation ball Can be avoided and damage to the detent ball can be prevented.

  Further, as in the invention described in claim 6, if the cross-sectional shape of the guide groove of the cage is formed in a Gothic arc shape and the corner portion of the guide groove is smoothly rounded, It is possible to prevent an excessive stress from being generated by an edge load caused by riding on the shoulder by contacting the shoulder portion of the guide groove.

  Further, as in the invention described in claim 7, if the cage is made of sintered metal formed by MIM, even if it has a high workability and a complicated shape, it can be easily and accurately obtained. Can be formed into shapes and dimensions.

  Further, as in the invention described in claim 8, if the retaining ring is formed by injection molding from a thermoplastic synthetic resin filled with a fibrous reinforcing material, it slides with strength over a long period of time. And wear resistance can be improved.

  An electric actuator according to the present invention includes a cylindrical housing, an electric motor attached to the housing, a speed reduction mechanism that transmits the rotational force of the electric motor via a motor shaft, and the speed reduction mechanism. A ball screw mechanism that converts the rotational motion of the electric motor into a linear motion in the axial direction of the drive shaft, and this ball screw mechanism is connected to the speed reduction mechanism and rotates via a rolling bearing mounted on the housing. A nut that is supported so as not to move in the axial direction and has a spiral thread groove formed on the inner periphery, and is inserted into the nut via a number of balls and is coaxially integrated with the drive shaft. A cylindrical actuator housing the drive shaft in the housing in an electric actuator having a screw shaft having a helical screw groove corresponding to the screw groove of the nut formed on the outer periphery. A bag hole is formed, extending in the axial direction on the inner periphery of the bag hole, forming a concave groove having an arc cross section, and is attached to the end of the screw shaft and the anti-rotation ball engaging the concave groove. And a cylindrical guide groove that extends in the axial direction on the outer periphery of the cage and faces the concave groove, and is formed by the guide groove and the concave groove. The ball is supported so as to be able to roll and the screw shaft is supported so as not to rotate with respect to the housing and to be movable in the axial direction, thereby reducing the number of parts and reducing the cost. An electric actuator with improved reliability can be provided by a detent mechanism that can be suppressed.

It is a longitudinal section showing one embodiment of an electric actuator concerning the present invention. It is a partial cross section perspective view which shows the rotation prevention part of FIG. (A) is a front view showing the screw shaft of FIG. 1, (b) is a longitudinal sectional view taken along line III-III of (a), and (c) is a perspective view showing a single holder of (b). FIG. (A) is principal part sectional drawing which shows the groove shape of the rotation prevention part of FIG. 1, (b) is principal part sectional drawing which shows the modification of (a). It is principal part sectional drawing which shows the comparative example of FIG. (A) is explanatory drawing which shows the other comparative example of FIG. 4, (b) is explanatory drawing which shows the state by which the load was loaded on the screw shaft of (a). (A) is principal part sectional drawing which shows the rotation prevention part of FIG. 1, (b) is principal part sectional drawing which shows the modification of (a). It is a longitudinal cross-sectional view which shows the modification of FIG.3 (b). It is a longitudinal cross-sectional view which shows the conventional electric actuator. FIG. 10 is a transverse sectional view taken along line XX in FIG. 9.

  A cylindrical housing, an electric motor attached to the housing, a speed reduction mechanism for transmitting the rotational force of the electric motor via a motor shaft, and a drive shaft for rotational movement of the electric motor via the speed reduction mechanism A ball screw mechanism that converts the linear screw motion into an axial linear motion of the motor, and the ball screw mechanism is connected to the speed reduction mechanism and is rotatable via a rolling bearing mounted on the housing, and is not movable in the axial direction. And a nut having a spiral thread groove formed on the inner periphery thereof, and a nut inserted into the nut via a number of balls, integrated with the drive shaft, and on the outer periphery thereof. A cylindrical bag hole for accommodating the drive shaft is formed in the housing, and an inner periphery of the bag hole is formed on the electric actuator. A concave groove extending in a direction and having an arc-shaped cross section, and a non-rotating ball that engages with the concave groove, and a cylindrical cage attached to an end of the screw shaft, and the screw shaft A recess is formed at the end of the outer periphery, and a pocket formed from an outer diameter corresponding to the concave groove and penetrating into the recess and having a diameter larger than the outer diameter of the anti-rotation ball is formed. A ball for rolling is accommodated in a freely rolling manner, and a guide groove having an arcuate cross section extending in the axial direction on the outer periphery of the retainer and facing the concave groove is formed. The guide groove and the concave groove A stop ball is held so as to be able to roll in a state of being sandwiched with a clearance, and the screw shaft is supported so as to be non-rotatable and axially movable with respect to the housing.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
1 is a longitudinal sectional view showing an embodiment of an electric actuator according to the present invention, FIG. 2 is a partially sectional perspective view showing a rotation preventing portion of FIG. 1, and FIG. 3 (a) is a screw shaft of FIG. FIG. 4B is a cross-sectional view taken along the line III-III in FIG. 4A, FIG. 4C is a perspective view showing the cage alone in FIG. 4A, and FIG. FIG. 5 is a cross-sectional view of the main part showing the groove shape of the detent 1; FIG. 5B is a cross-sectional view of the main part showing a modification of FIG. 6 (a) is an explanatory view showing another comparative example of FIG. 4, (b) is an explanatory view showing a state in which a load is applied to the screw shaft of (a), and FIG. 7 (a) is FIG. FIG. 8 is a cross-sectional view of a main part showing a rotation preventing part, FIG. 8B is a main part cross-sectional view showing a modification of FIG. 8A, and FIG. 8 is a vertical cross-sectional view showing a modification of FIG.

  The electric actuator 1 includes a cylindrical housing 2, an electric motor 3 attached to the housing 2, and a pair of spur gears 4 and 5 that transmit the rotational force of the electric motor 3 via a motor shaft 3a. A speed reduction mechanism 6, a ball screw mechanism 8 that converts the rotational motion of the electric motor 3 into a linear motion in the axial direction of the drive shaft 7 via the speed reduction mechanism 6, and a detent mechanism 9 for the drive shaft 7. Yes.

  The housing 2 includes a first housing 2a and a second housing 2b assembled to the end surface. An electric motor 3 is disposed inside the first housing 2a. The electric motor 3 is attached in a state where an outer ring of a ball bearing 18 attached to an outer diameter of a nut 16 described later is sandwiched between the first housing 2 a and the bearing bracket 10.

  A small spur gear 4 is attached to the motor shaft 3a of the electric motor 3 so as not to be relatively rotatable by press fitting. The large spur gear 5 is press-fitted into a nut 16 constituting a ball screw mechanism 8 described later, and meshes with the small spur gear 4.

  The ball screw mechanism 8 includes a screw shaft 15 having a spiral screw groove 15a formed on the outer periphery, and a nut 16 having a spiral screw groove 16a formed on the inner periphery thereof, facing the screw groove 15a of the screw shaft 15. And a large number of balls 17 accommodated in a spiral space formed by both screw grooves 15a and 16a so as to be freely rollable. The above-described large spur gear 5 is press-fitted and fixed to the outer periphery of the nut 16, and the ball bearing 18 fitted to the first housing 2 a and the bearing bracket 10 is positioned and fixed via a retaining ring 19, and is relatively relative to the axial direction. It cannot move and can rotate relatively.

  The cross-sectional shape of each thread groove 15a, 16a may be a circular arc shape or a Gothic arc shape, but here, it has a Gothic arc shape that allows a large contact angle with the ball 17 and a small axial clearance. Is formed. Thereby, the rigidity with respect to an axial load becomes high and generation | occurrence | production of a vibration can be suppressed.

  The nut 16 is made of case-hardened steel such as SCM415 or SCM420, and its surface is subjected to hardening treatment in the range of 55 to 62HRC by vacuum carburizing and quenching. Thereby, the buffing etc. for the scale removal after the heat treatment can be omitted, and the cost can be reduced. On the other hand, the screw shaft 15 is made of medium carbon steel such as S55C or case-hardened steel such as SCM415 or SCM420, and the surface thereof is hardened in the range of 55 to 62 HRC by induction hardening or carburizing hardening.

  The drive shaft 7 is integrally formed with a screw shaft 15 constituting the ball screw mechanism 8, and a hole 7 a for connecting to a link member (not shown) is formed at the left end portion of the drive shaft 7. A cylindrical through hole 13 and a bag hole 14 for accommodating the drive shaft 7 are formed in one housing 2a and the second housing 2b, respectively. The outer periphery of the drive shaft 7 is slidably supported by the bush 11 with respect to the first housing 2a, and a seal member 12 is mounted adjacent to the bush 11 so that the drive shaft 7 and the first housing 2 The space between the housing 2a is hermetically sealed to prevent dust and the like from entering from the outside.

  Here, a detent mechanism 9 is configured at the right end of the screw shaft 15. The anti-rotation mechanism 9 includes a pair of concave grooves 14 a and 14 a formed on the inner periphery of the bag hole 14, anti-rotation balls 20 and 20 that engage with the concave grooves 14 a and 14 a, and an end of the screw shaft 15. And a cage 21 attached to the section. As shown in FIG. 2, the pair of concave grooves 14a, 14a are formed in a linear shape extending in the axial direction so as to face the inner periphery of the bag hole 14 of the second housing 2b. Reference numeral 22 denotes a piece member 22 serving as a circulation member for the ball 17 attached to the nut 16.

  As shown in FIGS. 3A to 3C, the retainer 21 attached to the end of the screw shaft 15 is formed in a cylindrical shape, and a cylindrical portion 21 a fitted into the screw shaft 15, and this cylinder One end portion of the portion 21a is provided with a flange portion 21b extending radially outward. A concave portion 15b is formed at the end of the screw shaft 15. The cylindrical portion 21a of the retainer 21 is press-fitted into the concave portion 15b, and the flange portion 21b abuts against the end surface of the screw shaft 15, so that the retainer 21 is Positioning is fixed.

  A pocket 23 penetrating from the outer diameter to the recess 15b is formed at the end of the screw shaft 15. The pocket 23 is formed to have a diameter slightly larger than the outer diameter of the anti-rotation ball 20 and accommodates the anti-rotation ball 20 in a rollable manner. A guide groove 24 extending in the axial direction is formed on the outer periphery of the cylindrical portion 21 a of the cage 21. A pair of guide grooves 24 are formed on the opposing outer peripheral surfaces corresponding to the pockets 23 of the screw shaft 15 in a circular arc cross section. Then, the anti-rotation ball 20 is rotatably held in a state of being sandwiched with a slight gap by a concave groove 14a formed in the inner periphery of the bag hole 14 of the second housing 2b.

  The cage 21 is made of a sintered alloy that adjusts metal powder into a plastic shape and is molded by an injection molding machine. In this injection molding, first, metal powder and a binder made of plastic and wax are kneaded by a kneader, and the kneaded product is granulated into pellets. The granulated pellets are molded by so-called MIM (Metal Injection Molding), which is supplied to a hopper of an injection molding machine and pushed into a mold in a heated and melted state. A sintered alloy formed by such an MIM can be easily and accurately formed into a desired shape / dimension even if it has a high workability and a complicated shape.

  As the metal powder, a material that can be subsequently carburized and hardened, for example, C (carbon) is 0.13 wt%, Ni (nickel) is 0.21 wt%, Cr (chromium) is 1.1 wt%, Cu (copper) Exemplifies SCM415 which is 0.04 wt%, Mn (manganese) is 0.76 wt%, Mo (molybdenum) is 0.19 wt%, Si (silicon) is 0.20 wt%, and the rest is Fe (iron). Can do. The sleeve 18 is performed by adjusting the carburizing quenching and tempering temperatures. In addition to this, the sleeve 18 is made of a material containing 3.0 to 10.0 wt% of Ni and having excellent workability and corrosion resistance (FEN8 of Japanese Powder Metallurgy Industry Standard), or C of 0.07 wt%. %, Cr is 17 wt%, Ni is 4 wt%, Cu is 4 wt%, and the remainder is precipitation hardened stainless steel SUS630 made of Fe or the like. This SUS630 can appropriately increase the surface hardness in the range of 20 to 33 HRC by solution heat treatment, and can ensure toughness and high hardness.

  In this embodiment, the retainer 21 is fixed to the end of the screw shaft 15, and the anti-rotation ball 20 is accommodated in the pocket 23 formed at the end of the screw shaft 15. The anti-rotation ball 20 is sandwiched between the concave groove 14a formed in the inner periphery of the bag hole 14 of the second housing 2b and the guide groove 24 formed in the cylindrical portion 21a of the cage 21 with a slight clearance. Since the rotation-preventing ball 20 of the screw shaft 15 engages with the concave groove 14a of the bag hole 14 to prevent rotation with the axial guide of the screw shaft 15, aluminum is used. It is possible to provide an electric actuator that can reduce the sliding friction and wear of the second housing 2b made of a light alloy, improve the assemblability, and reduce the cost with a simple structure.

  Here, the cage 21 is formed with a flange 21b, and the flange 21b is abutted against the end surface of the screw shaft 15 to be positioned and fixed to the screw shaft 15. However, the present invention is not limited to this. Although not shown, a shaft retaining ring may be attached to the end of the cylindrical portion 21a instead of the flange portion 21b, and the cage may be positioned and fixed with respect to the screw shaft.

  The cross-sectional shape of the concave groove 14a formed in the bag hole 14 of the second housing 2b and the guide groove 24 formed in the cylindrical surface 21a of the cage 21 is as shown in FIG. It is formed in a so-called gothic arc shape having two curvature radii larger than the curvature radius of 20, and the rotation preventing ball 20, the concave groove 14a and the guide groove 24 are in angular contact at two points. As shown in (b), the cross-sectional shapes of the concave groove 14a 'and the guide groove 24' are formed in a so-called circular arc shape having a single curvature radius larger than the curvature radius of the anti-rotation ball 20. May be.

  Here, as shown in FIG. 5, the sectional shape of the concave groove 14a "formed in the bag hole 14 of the second housing 2b and the guide groove 24" formed in the cylindrical surface 21a of the retainer 21 is changed to a normal parallel key. When formed in a rectangular shape such as a groove, even if the load applied to the screw shaft is small, the anti-rotation ball 20 comes into contact with the shoulders of the concave groove 14a ″ and the guide groove 24 ″, and the edge load due to the shoulder climbing This is not preferable because excessive stress is generated and the anti-rotation ball 20 may be damaged. As described above, by forming the cross-sectional shapes of the concave groove 14a ′ and the guide groove 24 ′ into a Gothic arc shape or a circular arc shape, it is possible to avoid the shoulder ball 20 from climbing on the shoulder of the groove when the load is applied. It is possible to prevent damage to the anti-rotation ball 20. Here, “shoulder ride” means a phenomenon in which the contact ellipse due to the contact of the ball comes off from the shoulder portion of the groove, and “edge load” means excessive stress concentration occurring in the corner portion, A phenomenon that is one of the causes of early peeling and abnormal noise. In addition, it is preferable that the corner | angular part of a groove | channel is rounded smoothly.

  Further, as shown in FIG. 6A, in the case of the present embodiment in which the nut 16 rotates and the screw shaft 15 moves linearly, if the anti-rotation ball 20 constituting the anti-rotation mechanism is single, When a load is applied, the center of the screw shaft 15 (the cage 21) is eccentric from the center of the bag hole 14 of the second housing 2b as shown in FIG. There is a possibility that the straight traveling accuracy of the shaft 15 may be reduced. Therefore, in this embodiment, the rotation accuracy of the nut 16 and the rectilinear accuracy of the screw shaft 15 are achieved by using a plurality of anti-rotation balls 20 constituting the anti-rotation mechanism and disposing them at circumferentially even positions. Can be improved.

  Specifically, as shown in FIG. 7 (a), a pair of concave grooves 14a and 14a are formed to face the inner periphery of the bag hole 14 of the second housing 2b and extend in the axial direction, and the screw shaft. A retainer 21 is fixed to the end of 16, and a pair of guide grooves 24, 24 extending in the axial direction is formed on the outer periphery of the retainer 21 so as to face the recessed groove 14 a of the bag hole 14. And the rotation prevention ball | bowl 20 is accommodated so that rolling between these concave grooves 14a and the guide grooves 24 is possible. Thereby, even if a load is applied to the screw shaft 15, the center of the screw shaft 15 (the cage 21) is not decentered from the center of the bag hole 14 of the second housing 2 b, and accuracy can be improved. .

  Further, as shown in (b), three concave grooves 14a are formed on the inner periphery of the bag hole 14 'of the second housing 2b, and are held at the end of the screw shaft 16'. A container 21 'is fixed, and three guide grooves 24 are formed on the outer periphery of the retainer 21' so as to face the concave groove 14a of the bag hole 14 '. And the rotation prevention ball | bowl 20 is accommodated so that rolling between these concave grooves 14a and the guide grooves 24 is possible. As a result, the accuracy can be further improved.

  FIG. 8 shows a modification of the above-described detent mechanism. The anti-rotation mechanism includes a pair of concave grooves 14a and 14a formed on the inner periphery of the bag hole 14 of the second housing 2b, and anti-rotation balls 20 and 20 that engage with the concave grooves 14a and 14a. A retainer 26 attached to the end of the screw shaft 25 and a retaining ring 27 that retains the rotation-preventing balls 20 at an equal circumference are provided.

  The retainer 26 is press-fitted and fixed to a small-diameter step portion 25 a formed at the end of the screw shaft 25. The cage 26 includes a cylindrical portion 26a that is externally fitted to the small-diameter step portion 25a, and a flange portion 26b that extends radially outward at one end portion of the cylindrical portion 26a. A retaining ring 27 is press-fitted into the cylindrical portion 26a of the retainer 26, and the non-rotating ball 20 is rotatably accommodated and retained in a pocket 27a formed through the inner and outer diameters of the retaining ring 27. The retainer 26 is positioned and fixed by abutting against the step portion 25b of the screw shaft 25.

  A guide groove 24 extending in the axial direction is formed on the outer periphery of the cylindrical portion 26a of the retainer 26, and the anti-rotation ball 20 is slightly held by the concave groove 14a formed on the inner periphery of the bag hole 14 of the second housing 2b. It is held so that it can roll freely with a clearance. With such a detent mechanism, the sliding friction and wear of the second housing 2b can be reduced and the assemblability can be further improved and the cost can be reduced with a simple structure.

  Examples of the material of the retaining ring 27 include carbon steel such as S45C and carburized steel such as SCr420 and SCM415. In addition, for example, a fibrous reinforcing material such as GF (glass fiber) is 10 to 40 wt. % Of thermoplastic synthetic resin such as PA (polyamide) 66 filled may be formed by injection molding. Thereby, slidability and wear resistance as well as strength can be improved over a long period of time. Note that if the GF filling amount is less than 10 wt%, the reinforcing effect is not exhibited, and if the filling amount exceeds 40 wt%, the fibers in the molded product cause anisotropy and the density increases and the dimension is stabilized. This is not preferable because the toughness is lowered and the toughness is lowered and there is a risk of breakage due to the contact of the anti-rotation ball 20. In addition, as a fibrous reinforcement, not only GF but CF (carbon fiber), an aramid fiber, a boron fiber, etc. can be illustrated other than this.

  In addition to PA, thermoplastic synthetic resins called so-called engineering plastics such as PPA (polyphthalamide) and PBT (polybutylene terephthalate), polyphenylene sulfide (PPS), polyether ether ketone (PEEK), polyamide A thermoplastic synthetic resin called a so-called super engineering plastic such as imide (PAI), or a thermosetting synthetic resin such as phenol resin (PF), epoxy resin (EP), polyimide resin (PI), etc. Also good.

  The embodiment of the present invention has been described above, but the present invention is not limited to such an embodiment, and is merely an example, and various modifications can be made without departing from the scope of the present invention. Of course, the scope of the present invention is indicated by the description of the scope of claims, and further, the equivalent meanings described in the scope of claims and all modifications within the scope of the scope of the present invention are included. Including.

  An electric actuator according to the present invention includes a ball screw mechanism that is used in a drive unit of a general industrial electric motor, an automobile, or the like, and that converts a rotational input from an electric motor into a linear motion of a drive shaft via the ball screw mechanism. Applicable to electric actuators.

DESCRIPTION OF SYMBOLS 1 Electric actuator 2 Housing 2a 1st housing 2b 2nd housing 3 Electric motor 3a Motor shaft 4 Small spur gear 5 Large spur gear 6 Reduction mechanism 7 Drive shaft 7a Hole 8 Ball screw mechanism 9 Anti-rotation mechanism 10 Bearing bracket 11 Bush 12 Seal Member 13 Through-hole 14, 14 'Bag hole 14a, 14a', 14a "Recessed groove 15, 15 ', 25 Screw shaft 15a, 16a Screw groove 15b Recess 16 Nut 17, 20 Ball 18 Ball bearing 19 Retaining ring 21, 21' , 26 Cage 21a, 26a Cylindrical portion 21b, 26b Cage 22 Piece member 23, 27a Pocket 24, 24 ', 24 "Guide groove 25a Small diameter step 25b Step 27 Holding ring 51 Housing 51a Main body 51b Lid member 51c Recess 52 Output shaft 52a Cap hole 53 Nut 53a, 56a Thread groove 53b Groove 54 Bush 54a notches 55 sealing member 56 Ball screw shaft 57 Ball 58 bearing spacer 59 bearing 60 fixed member 61 retaining ring 62 gear 63 guide members 63a guide portion 63b engaging portion

Claims (8)

A cylindrical housing;
An electric motor attached to the housing;
A speed reduction mechanism for transmitting the rotational force of the electric motor via the motor shaft;
A ball screw mechanism that converts the rotational motion of the electric motor to the linear motion in the axial direction of the drive shaft via the speed reduction mechanism, and
This ball screw mechanism is connected to the speed reduction mechanism, and is supported by a rolling bearing mounted on the housing so as to be rotatable and immovable in the axial direction, and a nut having a helical thread groove formed on the inner periphery When,
The nut is inserted through a large number of balls, is integrated with the drive shaft coaxially, and is configured with a screw shaft in which a spiral screw groove corresponding to the screw groove of the nut is formed on the outer periphery. In the electric actuator,
A cylindrical bag hole for accommodating the drive shaft is formed in the housing, an axially extending groove is formed on the inner periphery of the bag hole, and a concave groove having an arc cross section is formed. A ball and a cylindrical cage mounted on the end of the screw shaft, and an axial guide groove extending in the axial direction on the outer periphery of the cage and facing the concave groove is formed; The guide groove and the concave groove hold the rotation-preventing ball so that the ball can roll freely, and the screw shaft is supported so as to be non-rotatable and axially movable with respect to the housing. Electric actuator.   A recess is formed at the end of the screw shaft, penetrates the recess corresponding to the recess from the outer diameter, and a pocket is formed having a diameter larger than the outer diameter of the detent ball, The non-rotating ball is rotatably accommodated, and the retainer includes a cylindrical portion that is fitted in the concave portion of the screw shaft, and a flange portion that extends radially outward at one end portion of the cylindrical portion. 2. The electric actuator according to claim 1, wherein the cage is positioned and fixed by abutting the end surface of the screw shaft.   A small-diameter step is formed at the end of the screw shaft, and the retainer is externally fitted to the small-diameter step, and a cylindrical retaining ring is press-fitted into the outer diameter of the retainer. The rotation-preventing ball is slidably accommodated in a pocket formed through the diameter, and the retainer abuts on a step portion of the small-diameter step portion of the screw shaft so that the retainer is positioned and fixed. The electric actuator according to claim 1.   The electric actuator according to claim 1, wherein a plurality of the anti-rotation balls are arranged at positions that are equally spaced around the circumference.   The electric actuator according to claim 1, wherein a cross-sectional shape of the concave groove of the bag hole is formed in a Gothic arc shape or a circular arc shape.   The electric actuator according to claim 1, wherein a cross-sectional shape of the guide groove of the cage is formed in a Gothic arc shape, and a corner portion of the guide groove is smoothly rounded.   The electric actuator according to claim 1, wherein the cage is made of a sintered metal formed by MIM.   The electric actuator according to claim 3, wherein the holding ring is formed by injection molding from a thermoplastic synthetic resin filled with a fibrous reinforcing material.

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